It will work good, just make sure you get one with external power (4 pin molex) since the card will tend to expect the 75W out of the slot you can get with PCIe.
Cablesaurus' brand new PCI->PCI-e adapter comes without a Molex. It's just an extension board you install in a PCI slot.
Maybe you are thinking about the PCI-e x1 to PCI-e x16 adapters.
I decided it's better to just get another board that has 2 PCIe x1 instead of older PCI
You can't use PCI-e x16 cards in normal PCI-e x1 slots without buying extender cables/adapters.
Unless you want to break the slots by sawing off the ends in which case the board loses it's warranty and resale value.